Criteria for the maintenance and improvement of water quality have been seriously reviewed recently, and there is an increasing need for more sophisticated water-processing technologies that ensure sufficient water quality. In particular, development of water-processing technologies for removing environmental hormones, such as dioxin, organochlorine compounds, such as trihalomethane, and harmful bacteria, such as Legionella and E. coli, is an urgent task.
The criteria for the prevention of Legionella infection specify that, should the number of detected bacteria of genus legionella above 102 CFU/100 ml in environmental water (such as cooling tower water) that residents are less likely to inhale the aerosol of, immediate measures, such as cleaning, be taken to reduce the number of bacteria.
The criteria also specify that the bacterial count must be kept less than 10 CFU/ml for the water for use in bathtub or shower that residents are likely to directly inhale the aerosol of.
On the other hand, clogging of the piping caused by scale deposits of inorganic compounds and metal corrosion has posed a serious problem, and there has been a great need in various industries for the development of new water-processing technologies to decompose and remove these materials.
Some of the conventional water-processing systems use photocatalysts. These conventional photocatalytic water-processing systems operate by taking advantage of photocatalytic activity of photocatalysts, such as titanium dioxide, that occurs as the catalysts are irradiated with UV rays in the water that requires processing.
One example of such systems is a fluid-processing system equipped with ozone-generating means and photocatalyst means. In this system, ozone is generated in the medium, or the water to be processed. Once the ozone is generated, a photocatalyst and the ozone are together exposed to UV rays, so that the ozone is decomposed by the catalyst and free radicals that can destroy contaminants are obtained (See, Patent Article 1).
A water-processing process is also proposed, as is a system for the process. This process involves a photocatalytic process in conjunction with an ozone process and processes organic materials in water to be processed into inorganic products (See, Patent Article 2).
All of the conventional photocatalytic water-processing technologies face the same problem, however. A long term use of the system results in the deposition of scale and oil on the silica glass jacket of the UV-lamp, decreasing the UV transmittance. The resulting decrease in the UV-lamp performance makes the long-term, stable processing of water difficult.
As a different approach, a water-processing system is also known that sterilizes water by electrochemically decomposing contaminants. In one such system, water in an electrolysis tank is oscillated and electrolysis is carried out to remove, or prevent the deposition of, scale deposits on the surface of the electrodes placed in the electrolysis tank. This system facilitates maintenance of the electrolysis tank (See, Patent Article 3).
However, this type of water-processing system requires some means for generating oscillation, such as means for generating bubbles or means for sonicating water provided within the electrolysis tank.
Another approach is to process water with chemicals. One such system is used in food processing plants to process waste water. This waste water-purification system includes a chemical processing unit in which pH is adjusted, flocculation is performed using chemicals, and waste particles grow and precipitate (See, Patent Article 4).
However, chemicals used in this type of water-processing system to decompose and remove COD and BOD components, hexane extracts, total phosphorus, and total nitrogen present in waste water requires a reaction tank for processing. In addition, the running cost of this system is high.
(Patent Article 1: Japanese Translation of PCT International Application No. Hei 10-511572)
(Patent Article 2: Japanese Patent Laid-Open Publication No. 2000-5747)
(Patent Article 3: Japanese Patent Laid-Open Publication No. 2003-24943)
(Patent Article 4: Japanese Patent Laid-Open Publication No. 2000-279995)